1. Technical Field
The present invention relates to systems and methods for selective control of the balance between nitrogen and oxygen content in the air in habitable and non-habitable areas of pressurized spaces within aircraft. More particularly, the invention relates to systems to alter the balance between oxygen and nitrogen in different areas of aircraft to create zones where the atmospheric composition more properly supports the needs of the zones. The invention accomplishes this zonal composition optimization by directing a higher percentage of the oxygen available in the air entering the aircraft into the habitable areas, while directing a higher percentage of the available nitrogen in the air into the non-habitable areas, especially those areas of greater flammability risk and/or limited access in case of fire.
2. Background Information
The reduced air pressure available in pressurized aircraft cabins results in molecular concentrations of oxygen that are far lower than those for which most passengers are physiologically adapted. This causes reduced levels of blood and tissue oxygenation (see FIGS. 1 and 2) and the initiation of physiological changes related to the body's efforts to compensate and adapt. The resulting physiological stresses include reduced respiratory effectiveness, compensatory increases in heart and respiration rates, increased levels of blood clotting factors, and increased production of red blood cells. These physiological changes result in, or contribute to, a variety of negative impacts, including but not limited to fatigue, reduced mental and physical performance, drowsiness, impaired visual acuity, impaired sleep, and possibly the formation of blood clots. In fact, it is well accepted that visual acuity has begun to fall off as early as 7500 feet, yet commercial airlines are legally permitted to maintain pressures equivalent to 8000 feet within the aircraft. As such, a certain compromise in the flight crew's capabilities have been determined acceptable, though not desirable. The present invention provides methods and systems for reducing, if not obviating, these and other detrimental affects suffered by passengers and flight crew on civilian aircraft.
Standard atmospheric pressure at sea level is 14.7 psia. The corresponding oxygen pressure (partial-pressure) at sea level is approximately 3.07 psia. When atmospheric pressure is reduced, air expands and the molecular concentration of oxygen and the other gases that make up air are proportionately reduced according to Dalton's Law.
Pressurized aircraft cabins provide air pressures ranging from approximately 10.91 psia (8000 ft equivalent cabin altitude) to 11.78 psia (6000 ft equivalent cabin altitude) when the aircraft are operating at their maximum cruise altitudes. These reduced cabin pressures result in oxygen partial pressures ranging (approximately) from 2.286 to 2.468 psia.
Aircraft pressurization systems maintain cabin pressure levels that allow passenger and crew habitation while the aircraft flies at altitudes far above those at which human beings could otherwise survive. Current pressurization systems maintain cabin air pressures between 74-80% of the standard sea level atmospheric pressure.
As a prophylactic against unexpected low-pressure experiences, and consequently low-oxygen conditions which could adversely affect performance, cockpit crew members are provided with pressure demand oxygen masks for use when the aircraft is unable to maintain adequate pressurization. The sources of direct oxygen may also be used in case smoke fills the cockpit, or under certain other scenarios as required by civil aviation regulations.
Emergency oxygen is provided in the passenger cabin in the form of drop down masks that activate automatically when air pressure in the cabin falls to levels at which passenger safety is at imminent risk. Therapeutic oxygen outlets are sometimes provided for use by passengers who require continuous supplemental oxygen due to medical conditions. Aircraft are also often equipped with portable “walk-around” oxygen bottles for the crew to use during brief periods when their duties require them to leave their seats while the aircraft is experiencing pressurization problems. A common problem of all of these supplemental oxygen delivery systems, however, is that they require tubes connected between an oxygen source and the delivery mask for the user. Such tubes, like other cords in the occupied compartments of an aircraft, have been recognized as hazards, particularly in emergency situations. It can be imagined that in an emergency situation where the environment is already chaotic, the deployment of potentially entangling oxygen delivery tubes and masks, including their elastic securement straps, detrimentally impacts the cabin environment.
As indicated above, conventional wisdom in aircraft design has focused on pressurization with regard to increasing the habitability of aircraft cabins. Traditionally, aircraft are pressured toward a sea-level equivalent; but in actuality, altitude equivalents on the order of 6000 to 8000 feet are actually achieved. Resultantly, a corresponding decrease in oxygen concentration has been accepted. Because these corresponding oxygen concentrations are generally suitable for maintaining perceivable occupant comfort, little attention has been directed toward consequential affects suffered by cabin occupants.
“Perceived comfort” is addressed because most passengers are unaware that certain physiological changes take place responsive to reduced oxygen concentration experienced onboard aircraft, including increased respiratory and heart rates. It is for this reason that many persons are advised not to fly. For instance, persons who have recently undergone surgery which makes them particularly vulnerable to these physiological changes may be advised not to fly. Still further, persons having predispositions to such ailments as heart attacks and strokes are often advised not to fly by their medical caretakers. Elderly persons, and others with unappreciated risk factors for such ailments do fly, but resultantly place themselves at undue risk of suffering a debilitating, or life-threatening incident. It is known that the decreased concentration of oxygen in aircraft have the potential for contributing to these incidents, but as discussed above, aircraft pressurization limitations have been heretofore viewed as a limiting constraint against their remedy.
The focus on pressure is due, at least in part, to the fact that airframes are not designed to accept greater levels of pressurization, which in turn produce greater differential pressures across the fuselage skin. In fact, this limitation associated with the airframe's capabilities to endure greater pressure differentials thereacross has traditionally imposed reduced oxygen levels on passengers because of the heretofore accepted limitation on pressurization. Still further, aircraft operators are resistant to increasing interior pressurization because it significantly increases operating costs and limits aircraft performance.
Deep Vein Thrombosis (DVT), a syndrome or condition which has recently garnered increased attention with respect to airline travel, poses significant risk to cabin occupants, as well as those businesses that are tied in with the industry. Because the incidence of deep vein thrombosis has caught the eye of the public, the press has capitalized thereupon and dubbed the syndrome as “economy class syndrome.” Heretofore, the focus has been on the confining and cramped nature of airline seats, particularly in economy class, and the restrictions that are resultantly imposed upon passenger mobility. Certain studies, however, have indicated that the cramped nature of smaller seats only contribute to the inducement of deep van thrombosis rather than cause it. In fact, those same studies tend to indicate that this malady stems primarily from other conditions experienced during airline travel.
Those factors which are either known or expected to contribute to the inducement of deep vein thrombosis include mobility restrictions which correspondingly reduce blood flow movements thereby placing a person at higher risk for forming blood clots, dehydration caused by the dry interior atmosphere of the aircraft and which can be exacerbated by the diuretic-effects of alcohol, and pressure related aspects. An increased tendency to develop blood clots as a result of conditions on an airliner are the hallmark of this syndrome. One aspect of great importance, but which has attracted less attention, is physiological effects caused by altitude adaptation. When exposed to reduced pressure and a corresponding reduction in oxygen concentration, the body immediately attempts to compensate. This phenomenon is well appreciated at least by athletes who often train at high altitudes to enhance their performance at lower altitudes. It is known that the body adjusts by making certain physical changes. Among others, the concentration of red blood cells is increased thereby improving the capacity for carrying oxygen. For airline passengers, the effect, however, is detrimental. It has been observed that persons who are exposed to the reduced pressure and oxygen levels that are experienced in-flight have a substantially immediate increase in certain clotting factors within their blood. This increase has been measured to vary between three and eight times the level present in persons immediately before flight. Such a high level response is equivalent to that which the body undergoes as a reaction to significant trauma or injury.
A hallmark of the present invention(s) is the previously unappreciated connection between the reduction in oxygen concentration experienced in-flight and the increased blood clotting factors that result and which ultimately impact the incidence of deep vein thrombosis suffered as a result of airline travel.
The invention also addresses fatigue, comfort and physiological stress issues which result from the practical limitations of aircraft pressurization systems, which existing oxygen delivery and control systems are either incapable of addressing or are not suitably configured.